Production of alkali metal nitrates



Patented Jan. 25, 1938 UNITED STTES PTENT OFF-IE PRODUCTION OF ALKALI METAL NITRATES New York No Drawing.

Application October 2, 1931,

Serial No. 566,583

Claims. (01. 23-102) This invention relates to the production of alkali metal nitrates, more particularly to a process for the preparation of sodium nitrate free from a carbonate of sodium and includes correlated improvements and discoveries whereby the production of pure sodium nitrate is facilitated.

The production of an alkali metal nitrate, for example, the production of sodium nitrate by the absorption of oxides of nitrogen in an alkaline liquor, gives, in the final stages, a resulting liquor which usually, in order to obviate the corrosive action of acid liquor on piping, is slightly alkaline due to sodium carbonate or caustic alkali. The liquor is then subjected to evaporation in order to concentrate it for subsequent crystallization of the sodium nitrate. During the evaporation procedure, the sodium carbonate and sodium bicarbonate that may be present tend to accumulate in the mother liquor and are held in solution. When the sodium nitrate has crystallized and is subsequently separated by filtration, the filtering operation does not completely remove all of the mother liquor from the crystale. The dry salt therefore contains a small amount of a carbonate of sodium. The presence of the small amount of this impurity is disadvantageous when the sodium nitrate is utilized for certain purposes, and accordingly it is an object of this invention to obviate such disadvantages.

It is an objectof this invention to provide a process for the treatment of basic liquors containing an alkali metal nitrate for the production therefrom of a satisfactory solid nitrate product. More particularly, it is an object of the invention to provide a process in accordance with which sodium nitrate substantially free from sodium carbonate and sodium bicarbonate may be obtained readily and eificiently on a commercial scale.

Other objects of the invention will in part be obvious and will in part appear hereinafter.

The invention accordingly comprises the several steps and the relation of one or more of such steps with respect to each of the others thereof, which will be exemplified in the process hereinafter disclosed, and the scope of the invention will be indicated in the claims.

In the practice of the invention, an alkali metal nitrate liquor obtained in the course of manufacture, and particularly a sodium nitrate liquor containing a carbonate of sodium may be reacted With an ammonium salt. Examples of salts suitable for addition to the nitrate liquor in accordance with this: invention are ammonium nitrate, ammonium sulfate, ammonium phosphate, or ammonium chloride. It is preferred to employ ammonium nitrate which accomplishes the removal of the sodium carbonate Without introducing any impurity into the sodium nitrate. The addition of the salt may be made during the evaporation or concentration of the liquor prior to crystallization of the sodium nitrate or the salt may be introduced prior to-the evaporation of the'liquor. There is thereby effected a decomposition of the carbonate of sodium with the formation of ammonium carbonate, which in a boiling solution of sodium nitrate decomposes into ammonia and carbon dioxide which pass 01? from the boiling solution.

By employing a salt of the type described above for the treatment of sodium nitrate liquor containing sodium carbonate, it is possible to remove the sodium carbonate in a simple efficacious manner.

As an illustrative embodiment of a manner in which the process may be carried out in practice, the following example is given:

A sodium nitrate liquor containing, for example, an amount of a carbonate of sodium equivalent to about 2 grams per liter of NazCOs is passed into an evaporator, as a three-effect multiple evaporator, and therein concentrated. This sodium nitrate liquor during the concentration in the evaporator, and more particularly in the third, or last effect thereof, is reacted with ammonium nitrate. The ammonium nitrate is added in the proportions of about 3 grams ammonium nitrate per liter of original solution before evaporation. This corresponds to stoichiometric proportions of ammonium nitrate and sodium carbonate in solution. There is thereby eiiected a reaction with the sodium carbonate and/or sodium bicarbonate which may be present, and their removal whereby the carbonate is prevented from passing into the mother liquor and being present in the sodium nitrate whenit is obtained in dry, crystalline form. The sodium nitrate which crystallizes from the evaporated liquor, is separated by filtration and subsequently dried in a suitable drier.

The ammonium salt may also be added to the nitrate liquor by forming the salt in situ within the liquor. Thus, for example, an acid nitrate liquor containing free nitric acid and prior to final addition of sodium carbonate may be treated with ammonia to form the desired quantity of ammonium nitrate by reaction'with a portion of the free nitric acid in the liquor and the residual nitric acid then reacted with additional sodium carbonate." During the concentration of the thus treated liquor, the ammonium nitrate reacts with the sodium carbonate and/or sodium bicarbonate which may be present to remove the carbonate and result in the production of a sodium nitrate substantially free from carbonate.

By the process above described, the sodium carbonate and/or sodium bicarbonate content of a sodium nitrate liquor may be substantially entirely removed and such removal is considered to be brought about in the manner set forth by the following equations:

As will appear from the above equations the amount of the salt added will be preferably that which is required to fully react with the car.- bonate of sodium present in the sodium nitrate liquor.

Sodium nitrate produced in the foregoing manner is substantially free from a carbonate of sodium and a nitrate containing not more than 0.02 per cent. of sodium carbonate may be obtained on a commercial scale.

Since certain changes may be made in carrying out the above process without departing from the scope of the invention, it is intended that all matter contained in the above description shall be interpreted as ilustrative and not in a limiting sense. For example, when the nitrate liquor contains a base such as sodium hydroxide to render it slightly basic in reaction and non-corrosive to the evaporator, the liquor may be treated in accordance with this invention by the addition thereto ofan ammonium salt and heating to evolve ammonia, thus removing excess base from the liquor and enabling the manufacturer to produce a satisfactory crystalline sodium nitrate product. This invention is likewise applicable to the production of alkali metal nitrates in general, and in particular to potassium nitrate from a basic liquor containing the same together with potassium carbonate or other alkaline material.

I claim:

1. In a process for the production of an alkali metal nitrate from an aqueous solution of the same containing a small proportion of an alkaline material from the group consisting of the alkali metal carbonates and hydroxides, that improvement which comprises treating said solution with an inorganic ammonium salt and heating the thus treated solution to concentrate it until said alkaline material is substantially completely removed therefrom.

2. In a process for the production of an alkali metal nitrate from an aqueous solution containing the same together with a small proportion of an alkaline material from the group consisting of the alkali metal carbonates and hydroxides, that improvement which comprises treating said solution with an ammonium salt belonging to the group consisting of ammonium nitrate, ammonium, sulfate, ammonium chloride and ammonium phosphate and heating the thus treated solution to evaporate water therefrom until said alkaline material is substantially completely removed from the solution.

3. In a process for the production of an alkali metal nitrate from an aqueous solution containing the same together with a small proportion of an alkaline material from the groupconsisting of the alkali metal carbonates and hydroxides, that improvement which comprisestreating said solution with an ammonium salt belonging to the group consisting of ammonium nitrate, ammonium sulfate, ammonium chloride and ammonium phosphate in amount corresponding to about stoichiometric proportions to the alkaline material present in the solution and heating the thus treated solution to evaporate water therefrom until said alkaline material is substantially completely removed therefrom.

4. In a process for the production of sodium nitrate from an aqueous solution containing the same together with a small proportion of an alkaline material from the group consisting of sodium carbonate and sodium hydroxide, that improvement which comprises reacting said alkaline material in the solution with an ammonium salt belonging to the group consisting of ammonium nitrate, ammonium sulfate, ammonium chloride and ammonium phosphate and heating the thus treated solution to evaporate water therefrom until said alkaline material is substantially completely removed from the solution.

5. In a process for the production of sodium nitrate from an aqueous solution containing the same together with a small proportion of an alkaline material from the group consisting of sodium carbonate and sodium hydroxide, that im provement which comprises treating said solution with an ammonium salt belonging to the group consisting of ammonium nitrate, ammonium sulfate, ammonium chloride andammonium phosphate in amount corresponding to about stoichiometric proportions to the alkaline material present in the solution and heating the thus treated solution to evaporate water therefrom until said alkaline material is substantially completely removed therefrom.

6. In a process for the production of sodium nitrate from an aqueous solution of the same containing a small proportion of an alkaline material-from the group consisting of sodium carbonate and sodium hydroxide, that improvement which comprises reacting said alkaline material in the solution with ammonium nitrate and heating the solution under conditions such that ammonia is evolved from the solution until the alkaline material is substantially completely removed therefrom.

7. In a process for the production of sodium nitrate from an aqueous solution of the same containing a small proportion of an alkaline material from the group consisting of sodium carbonate and sodium hydroxide, that improvement which comprises reacting said alkaline material in the solution with ammonium nitrate and heating the solution to evaporate it until said alkaline material is substantially completely removed therefrom.

8. In a process for the production of sodium, nitrate from an aqueous solution of the same containing a small proportion of sodium carbonate, that improvement which comprises reacting the sodium carbonate in the solution with ammonium nitrate and heating the solution to evaporate water therefrom until the solution is substantially completely freed of carbonate.

9. In a process for the production of sodium nitrate from an aqueous solution of the same containing a small proportion of sodium carbonate, that improvement which comprises reacting the sodium carbonate in the solution with about stoichiometric proportions of ammonium nitrate, and heating the solution to evaporate water therefrom until the solution is substantially freed of carbonate.

10. In a process for the production of sodium nitrate that improvement which comprises reacting ammonia With an aqueous sodium nitrate solution containing free nitric acid, adding sodium carbonate to the thus treated solution until it is basic but contains sufficient ammonium salt to fully react with the sodium carbonate present and heating said basic solution to evaporate water therefrom until the carbonate is substantially completely removed from the solution.

ALFRED STEVENS DENNY. 

